1. Field of the Invention
This invention relates to the field of radiation cameras, and particularly to a system and method for controlling the exposure of the radiation camera image to an image sensing device.
2. Description of the Prior Art
Radiation cameras are known which receive radiation stimuli emanating from a subject and convert them into a detectable display image representing the intensity and location of those stimuli.
Such radiation cameras are of use in medical diagnostic applications. It is known that certain organs and tissues of animal bodies have an affinity to accumulate particular radioactive isotopes. When an isotope is injected into the body, it tends to accumulate in a disproportionate amount in the particular organs and tissues having the affinity for it. When the organ having the affinity for the isotope is known, radiation due to the accumulation of the isotope in the organ can be observed by a radiation camera, and an image of the organ, or of particular healthy and/or diseased tissues of the organ, can be derived. Such images are of significant value in determining the existence and extent of disease or injury.
Known radiation cameras typically each include a detector responsive to radiation from the subject to produce radiation signals which electrically represent the position and intensity of the detected stimuli. Such cameras further include a display apparatus which is responsive to the radiation signals generated by the detector to produce the image corresponding to the pattern of detected stimuli. Such a radiation camera is disclosed in U.S. Pat. No. 3,784,819, to Martone, et al.
A typical display apparatus includes a cathode ray oscilloscope which is connected to the detector, such that the image produced by the radiation camera is a visible image on the tube face of the oscilloscope. Such display apparatus also includes a feature whereby the intensity of the visual display may be adjusted independently of the intensity of the radiation stimuli which cause the production of the image. Such images produced on the tube face of a cathode ray oscilloscope are not permanent in nature.
Notwithstanding the lack of permanency of the images, it is often desirable to make a permanent record of such images, or to convert the images into different formats for auxiliary observation and/or recording. It is, therefore, a common practice to provide radiation cameras with image sensing cameras of various types which may be positioned relative to the display apparatus of the radiation camera so that the image sensing camera may be exposed to record the generated image. Such image sensing cameras are frequently photographic cameras, including a structure for holding a piece of light sensitive film in a position disposed toward the image generated by the display apparatus. It is known to control the aperture of such photographic cameras to govern the amount of light incident on the film from the image, so that the exposure may be limited in accordance with the film sensitivity.
It is also known to expose the image to a television image sensing camera, for transmission of the image to a remote location. Such television cameras also often incorporate aperture control for governing the amount of exposure in accordance with the sensitivity of the instrument.
In order to make an image of the radiation emanating from a subject, the radiation camera is operated for a time, during which time a predetermined quantity of radiation stimuli cumulatively detected is used to generate the display image. The quantity of radiation used to make the image is known as the information density of the exposure. The display image thus generated is projected onto the image sensing device, such as the photographic camera.
For a given oscilloscope intensity setting, the information density of the exposure interval must be within a specified range for the picture to have optimum quality, because the information density has a significant relationship to the quality of the image obtained. If the information density is too small, insufficient data will be detected by the radiation camera, and the radiation camera display and the resulting photographic image will be faint and of poor resolution. If the information density is too great, the light sensitive film of the photographic camera will be over-exposed, the image will have poor resolution, and the background and scatter radiation will obscure the desired image of the organ or tissue being examined.
It is necessary to vary the value of the information density input to the radiation camera according to the type of tissue being examined and the isotope being used. The brightness of the display image, however, varies with the information density, and this often causes over or under exposure of the image on the photographic image sensing camera.
An effective way to compensate for this potential over or under exposure is to independently adjust the brightness of the cathode ray oscilloscope display apparatus. Such adjustments can enable an operator to derive an image brightness for properly exposing the film to get a good quality photograph of the image.
In the past, this independent intensity adjustment has necessarily been made by trial and error. The operator, after selecting the appropriate information density to derive the proper information from the radiation stimuli, must independently adjust the intensity of the image produced by the display apparatus. This technique causes waste of time, is imprecise, requires skill, and often yields poor pictures despite the operator's best efforts.
This procedure is further complicated by the necessity for coordinating this brightness adjustment with the sensitivity of the film used in the photographic image sensing camera, and with the exposure aperture. Thus, the operator is faced with the task of coordinating the three variables of image display brightness, exposure aperture, and film sensitivity, with the fourth variable, information density.
It is therefore an important purpose of this invention to provide a system and method for assisting the operator in precisely selecting the proper brightness level for the display image so as to derive an acceptable photograph, notwithstanding variations which necessarily must occur in the formation density necessary to gather sufficient radiation stimuli for creating the image, and variations in the aperture and film sensitivity of the photographic sensing camera.
Known radiation cameras require the operator to center the revelant portion of the image on the display apparatus presentation format by trial and error. It is another purpose of this invention to provide an improved method and system for facilitating the location of the image produced by the display apparatus at a predetermined point on that apparatus for best viewability.